Table of Content
- Packet Building Examples
- Sending Packets
- Exercise 1. Sending UDP Datagram in ScaPy
- Remark: Getting Help from ScaPy
We can use ScaPy to build and transmit network packets. To build a network
packet, we can ScaPy’s division operator
/. ScaPy defines the division
operator as the operator to binds packet headers and pay load together
with respect to the layered protocol architecture.
Packet Building Examples
To build an IP packet, we do this in ScaPy,
>>> packet=IP() >>> hexdump(packet) 0000 450000140001000040007CE77F000001 E.......@.|..... 0010 7F000001 .... >>>
where we first build a “default” IP packet with no payload.
Since a payload of an IP packet comes an application or an upper layer
protocol, we can use the
/ operator to fill the IP packet with
>>> packet = packet / 'Hello, World!' >>> hexdump(packet) 0000 450000210001000040007CDA7F000001 E..!....@.|..... 0010 7F00000148656C6C6F2C20576F726C64 ....Hello, World 0020 21 ! >>>
where the syntax of expression
packet / 'Hello, World!' is that the lower
layer on the left and the upper layer is on the right
Perhaps, this convention is more apparent when we build a TCP packet, for instance as follows,
>>> packet = IP()/TCP()/'Hello, World' >>> hexdump (packet) 0000 450000340001000040067CC17F000001 E..4....@.|..... 0010 7F000001001400500000000000000000 .......P........ 0020 500220007144000048656C6C6F2C2057 P. .qD..Hello, W 0030 6F726C64 orld >>> packet.pdfdump(layer_shift=1)
What if we wish to build a UDP datagram that we intend to send it to another host via an Ethernet interface,
>>> packet=Ether(dst='FF:FF:FF:FF:FF:FF')/IP(dst='127.0.0.1')/UDP(dport=50001)/Raw(load='Hello, World!')
send function to send a packet
Exercise 1. Sending UDP Datagram in ScaPy
Let’s consider the following task.
- Can you construct a UDP datagram carrying a short message and send it to an end point on another host?
- Can you use ScaPy to receive (or sniff) the datagram?
- Can you write a Socket receiver program to receive the packet on the other host?
Remark: Getting Help from ScaPy
First, start ScaPy, like,
$ sudo scapy3
Try these commands in ScaPy, one at a time. What do you observe? Is it helpful?
ls() ls(TCP) ls(UDP) ls(IP) ls(IPv6) ls(ICMP) ls(Ether) ls(Dot11) lsc() help(send) help(sendp)